The present invention relates to a rotary actuator with a cushion mechanism which can stop an oscillating and rotating main axis at an end of a rotational stroke in a cushioning manner.
In a rotary actuator generating a rotational force due to an air pressure, there is a rack and pinion type. The rack and pinion type rotary actuator is structured such as to drive a rack in an oscillating manner and rotate a pinion and a main axis fixed to the pinion in an oscillating manner by slidably inserting a piston with the rack into a cylinder tube, engaging the pinion with the rack and applying an air pressure to a pressure chamber sectioned and formed in both sides of the piston.
In the conventional rotary actuator of this kind, in order to absorb an impact force generated by an inertia energy of the piston when the main axis stops at the rotary stroke end, a mechanical cushion mechanism provided with a damper or the like is provided. However, the mechanical cushion mechanism mentioned above has problems that an impact sound is generated at a time of stopping, a deterioration due to abrasion is easily facilitated in the collided portion and parts such as a damper or the like are protruded outward so as to stand in the way. These problems mentioned above can be solved by providing an air pressure type cushion mechanism in place of the mechanical cushion mechanism mentioned above.
As the air pressure type cushion mechanism mentioned above, there has been conventionally known a structure made such as to temporarily seal a cushioning air within a pressure chamber in an exhaust side so as to increase a pressure of the air at a time of operating a piston sliding within a cylinder tube and reduce a speed of the piston by an exhaust pressure so as to stop the piston at a stroke end in a cushioning manner. The structure is made such that an exhaust passage of the air is closed by fitting a cushion ring provided in a piston side into a cushion packing within the cylinder tube in front of the stroke end, the sealed air is introduced to a throttle valve, and a piston back pressure converts a kinetic energy supplied from the piston into an air compression energy in correspondence to a throttle adjusting amount so as to obtain a speed reduction force.
However, in the cushion mechanism utilizing a piston back pressure, since it is required that the cushion ring having a required length is provided in at least one side of the piston and a long empty chamber to which the cushion ring is inserted and fitted is provide in the cylinder tube in view of the structure, the problem that an axial length of the cylinder becomes long is pointed out. Accordingly, when using the cushion mechanism in the rack and pinion type rotary actuator, the rotary actuator which tends to be long in a direction perpendicular to the main axis in view of the structure is further made longer in the direction.
A main object of the present invention is to provide a rotary actuator of a rack and pinion type provided with an air pressure type cushion mechanism.
Another object of the present invention is to structure a rack and pinion type rotary actuator having a large length in a direction perpendicular to a rotational main axis in view of a structure such that the length does not become longer even by attaching the cushion mechanism.
The other object of the present invention is to provide a rotary actuator with a cushion mechanism of a rack and pinion type in which a compact, simple and inexpensive structure can be obtained by omitting a long cushion ring and a long empty chamber to which the cushion ring is inserted and fitted.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a rack and pinion type rotary actuator having a rack driven in an oscillating manner by an air pressure, a pinion engaged with the rack, and a cushion mechanism for stopping the rack to at least one normal or inverse stroke end in a cushioning manner.
The cushion mechanism mentioned above has an exhaust port open to a pressure chamber for driving the rack at a position close to a chamber end rather than a port hole, a flow amount adjusting mechanism for restricting a flow amount of the exhaust air discharged from the exhaust port, and a cushion packing mounted to an outer peripheral surface of the piston and operating so as to shut the port hole from the pressure chamber immediately before the piston reaches the stroke end, thereby discharging the air within the pressure chamber through the flow amount adjusting mechanism.
In the rotary actuator in accordance with the present invention having the structure mentioned above, the rack is driven in an oscillating manner and the pinion rotates in an oscillating manner following thereto, by alternately supplying the compressed air to the pressure chambers in both sides of the rack from the port. At this time, a speed reducing and stopping operation is performed by the cushion mechanism at the stroke end of the rack in the following manner. That is, the compressed air within the pressure chamber in the exhaust side is at first discharged mainly through the port hole, however, when the rack moves close to the stroke end and the cushion packing moves over the port hole, the port hole and the pressure chamber are shut and the exhaust air from the pressure chamber is discharged in a limited manner through the flow amount adjusting mechanism only from the exhaust port. Accordingly, the pressure of exhaust air within the pressure chamber is increased, and the rack reaches the stroke terminal end while the speed of the rack is reduced due to the back pressure corresponding to the increased exhaust pressure.
Therefore, in accordance with the present invention, it is possible to obtain a rack and pinion type rotary actuator provided with an air pressure type cushion mechanism. Further, since it is not necessary to provide the long cushion ring and the long empty chamber to which the long cushion ring is inserted and fitted, which are provided in the conventional cushion mechanism, it is possible to reduce a length of the actuator in an axial direction of the cylinder at a degree thereof, so that it is possible to obtain an actuator having a compact and simple structure.
In accordance with a preferable embodiment of the present invention, the exhaust port mentioned above is connected to one port via the flow amount adjusting mechanism.
The flow amount adjusting mechanism is formed by a throttle hole for limiting a flow amount of the exhaust air discharged from the pressure chamber mentioned above, and a check valve which prevents the exhaust air discharged from the pressure chamber from flowing but allows a flow of a supplied air flowing into the pressure chamber is provided in parallel to the throttle hole.
In accordance with a particular embodiment of the present invention, a valve chamber connecting the exhaust port to the port is formed in the casing and a hole member having the throttle hole is received within the valve chamber via a lip seal forming the check valve between the lip seal and a chamber wall, whereby the throttle hole and the check valve are assembled within the valve chamber.
The rotary actuator in accordance with the present invention may be of a single rack type having one rack or may be a double rack type having two racks.
In the double rack type rotary actuator, a first pressure chamber and a second pressure chamber are sectioned in both sides of each of two racks, the first pressure chamber of the first rack and the second pressure chamber of the second rack are connected to a first port, and the first pressure chamber of the second rack and the second pressure chamber of the first rack are connected to a second port. Further, two sets of cushion mechanisms are provided for respectively stopping two racks mentioned above to one stroke end in a cushioning manner.
In accordance with a preferable particular embodiment of the present invention, a casing of the actuator has end covers at both ends respectively, two ports mentioned above are provided in one first end cover, the flow amount adjusting mechanism in two sets of cushion mechanisms mentioned above is assembled in another second end cover, the exhaust port open to the second pressure chamber is provided, the port and the flow amount adjusting mechanism are communicated with each other through a through hole formed in the casing, and the port hole is branched from the through hole so as to be open to a hole surface of the cylinder hole.